1. Technical Field
The present invention relates in general to a method and system for using a Fibre Channel. More particularly, the present invention relates to an improved system and method for opening and closing a Fibre Channel device to improve device efficiency within the Fibre Channel fabric.
2. Description of the Related Art
Computer systems in general and International Business Machines (IBM) compatible personal computer systems in particular have attained widespread use for providing computer power to many segments of today's modern society. Computer systems typically include a system processor and associated volatile and non-volatile memory, a display area, input means, and often interfaces, such as a network interface or modem, to other computing devices.
One of the distinguishing characteristics of these systems is the use of a system board to electrically connect these components together. These computing devices are information handling systems which are designed primarily to give independent computing power to a single user, or a group of users in the case of networked computing devices. Personal computing devices are often inexpensively priced for purchase by individuals or businesses. Nonvolatile storage devices such as hard disks, CD-ROM drives and magneto-optical drives are considered to be peripheral devices. Computing devices are often linked to one another using a network, such as a local area network (LAN), wide area network (WAN), or other type of network. Computer systems can also be interconnected using a Fibre Channel network. By linking to other computer systems, a computing device can use resources owned by another computing device. These resources can include files stored on nonvolatile storage devices and resources such as printers and storage area networks (SANs).
Data Storage has become an increasingly important issue for business people and IT professionals. Organizations store records in databases regarding customers, products, competitors, and other records. This storage space becomes expensive when more data is stored. These expenses can be potentially prohibitive for small businesses who must employ people to manage the data, purchase storage equipment and software, and ensure that the data is properly protected from disaster or storage device failure. A solution to this problem comes in the form of an emerging technology called Fibre Channel. Fibre Channel can be used to connect devices to each other, including connecting computer systems to storage devices such as SAN devices.
Fibre Channel is a high speed (100 to 1000 Mbps currently, with speeds increasing quickly over time) medium used for data transfer and storage. It is essentially a serial data channel preferably created over fiber optic cabling. Fibre Channel provides a logical bi-directional, point-to-point connection between a host and a device. Similar to networking technologies using local area network (LAN) or wide area network (WAN) configurations, Fibre Channel also is used to connect PCs, servers, printers, and storage devices. Because Fibre Channel allows the use of fiber optic cabling, connections along a Fibre Channel network makes it possible to transfer data at greater distances. In addition, Fibre Channel makes high-speed data transfers possible. Fibre Channel also provides increased bandwidth over communication channels.
Channels and networks are the two primary ways that data is transferred between devices. Such devices include processors and peripherals such as printers and storage devices. Channels transfer data through switched or direct point to point connections. Channels work by creating a fixed connection between the source and destination devices until the transfer is complete. Channels transfer data at high speeds and are very economical. Networks (i.e., LAN or WAN), on the other hand are collections of nodes such as processors, print devices, and workstations. Connections on networks are typically slower than those made via channels. Also, because networks are software intensive, they are much more expensive due to upgrade and compatibility issues. Channels work best among few devices and connect via predefined addresses. Networks, on the other hand, can handle multiple requests among multiple connections.
Fibre Channel is hybrid of both network and channel methods. Consequently, Fibre Channel is often considered a new I/O (input/output) interface that combines the best of networks and channels. In addition, Fibre Channel systems can be configured in different ways depending on needs of the user, thus providing flexibility in an ever changing systems environment.
Devices are connected on Fibre Channel systems using various interconnection topologies. Interconnection devices available for use on Fibre Channel are switches, hubs, and bridges. The ability of Fibre Channel to use different interconnect devices makes it scalable depending on user needs. For small Fibre Channel networks, hubs and bridges may be used for connecting devices in a topology called Fiber Channel Arbitrated Loop (FC-AL). As Fibre Channel networks get larger and network demands increase, switching may be implemented. A switched Fibre Channel network is called a “fabric.” A fabric is simply the underlying switching architecture used by a Fibre Channel switch. A fabric may contain many loops interconnected with switches.
SCSI (Small Computer System Interface) is a common storage interface for I/O systems. However, SCSI environments have challenges, including limited bandwidth, limited distances, and limited device connections. An advantage of Fibre Channel is increased transmission speed and transmission distance. Data can be sent over longer distances using Fibre Channel because of fiber optic cabling, whereas SCSI only allows data transfers at distances up to 30 meters. Another advantage of Fibre Channel is that it allows millions of device connections, whereas SCSI adapters are usually allowed only eight to sixteen device connections.
Although the ideal medium for Fibre Channel is fiber optic cabling, Fibre Channel can also be used with a variety of cable types such as copper, coaxial cables or Unshielded twisted pair (UTP) wires. Fiber optic cabling is generally preferred on a Fibre Channel system for purposes of increased speed and reliability. Fiber optic cabling works by using photons to transmit digital signals. A laser light connected to a device pulses in binary format (0's and 1's). A light emitting diode (LED) codes and transmits the signal from one end of the cable. This signal is subsequently decoded at the other end of the cable by a photo-detector connected to the receiving device. Fiber optic cables do not have the same challenges that are associated with copper cabling. These challenges include attenuation (loss of signal strength) and noise. Fiber optic cables are also more secure than copper cables because crosstalk does not occur with Fiber Optic cables (crosstalk is interference caused by a signal transferring from one circuit to another, as on a telephone line). This insures that data being transferred across a network gets to its destination intact which makes the stored data more reliable for the user.
Fibre Channel technology makes use of classes of service to define messaging types (communication between devices). According to the ANSI standard, a Fibre Channel system's classes of service can be 1, 2, 3, 4 or 6. These classes make it possible to configure Fibre Channel systems according to the needs of the users.
In a class 1 configuration, there is a dedicated channel between two connection devices. In this configuration, if a host and a device are connected, no other host uses the connection. The advantage of using service class 1 is speed and reliability which is an excellent combination for mass storage use such as in a data library. Class 2 is known as a “connectionless” service. Class 2 provides a frame-switched link that guarantees delivery of packets from device to device. It also provides packet receipt acknowledgments. In this configuration, bandwidth is shared among several devices, as there is no dedicated link. The third Fibre Channel service class (Class 3) is called “unacknowledged connectionless service” and is often used for messages that do not need to be acknowledged, as there is no acknowledgement with a Class 3 configuration. Class 4 is called “fraction bandwidth connection oriented” and allows a device to reserve a portion of the overall bandwidth and use the reserved portion to create a dedicated channel between devices (similar to Class 1, except only part of the available bandwidth is used for the dedicated channel). Class 6 is called “multicast” and is used for one-to-many broadcast communications over the Fibre Channel network. There is an additional Fibre Channel service class called “intermix,” which creates a dedicated connection like that of class one, but it also allows class 2 traffic to access the link. This method is efficient and allows for greater bandwidth because more than one connection can access the system at any time.
The Fibre Channel Structure, or architecture, is set forth in the table below. The layers in the table represent a different function that exists within a Fibre channel system.
LayerFunctionFC-0Physical characteristic specificationsFC-1Encoding/DecodingFC-2Data Transfer Sequence Management/Data FramingFC-3Bandwidth ManagementFC-4Application/Protocol Management
FIG. 1 shows various topologies that are used with Fibre Channel. These topologies include Loop topology 110, Point-to-Point topology 120, and Fabric topology 100. Within these topologies, several connection types can exist between two Fibre Channel nodes. These include point-to-point connections, cluster connections, and switched connections. Point-to-point connections are typically used for high-speed connections at maximum distances. In this type of connection, no other device accesses the connection while two devices are communicating. Cluster connections connect multiple devices such as workgroup clusters, while switched connections allow more than one simultaneous connection of devices. A transceiver is a device that connects cabling to devices on any network or system and makes data transmission possible between devices.
Fabric topology 100 permits multiple paths between two ports on the Fabric. Loop topology 110, on the other hand, uses one active circuit at a time. Loop and fabric topologies can be combined. In addition, a fabric may contain one or more loops. If a link in a point-to-point topology 120 fails, communication between that pair of ports stops, while communication between other point-to-point connected Ports continues.
Fabric topology 100 includes a switch or a network of switches. These switches create the connections between devices in order for frames to be transported between the connections based on specifying a destination identifier (ID). If the destination ID is determined to be invalid, the fabric rejects the transmission. The function of the Fabric is similar to that of a telephone system, which provides a complete, low-cost connectivity solution. Fibre Channel establishes temporary, direct, and full-bandwidth connections between devices. Fibre Channel makes use of unique address identifiers, similar to telephone numbers, to connect processors to other processors or peripherals at distances currently reaching up to 10 km.
Storage Area Networks are increasing in popularity due to high demand by users who need to store large volumes of data. In addition, the cost of magnetic media that comprise Storage Area Networks continues to fall, thus making large data networks both attractive and feasible. The data in a Storage Area Network might be used in data warehouses or decision support systems used by businesses. There are also new applications for Storage Area Networks such as fault tolerant RAID clusters. Storage Area Networks can operate using network interconnect devices such as SCSI, Fibre Channel, HIPPI, or Sonnet. A SAN is a group of storage devices connected via a network of connections to hosts machines across greater distances than are possible on a traditional LAN. Storage Area Networks enable users to store large volumes of data at remote locations. These remote locations, called libraries, make it possible for businesses to store their data, whether for the purpose of creating backups or moving data management away from the primary site. If used for storage, a SAN will typically contain many high capacity Redundant Arrays of Inexpensive Disks (RAID) devises configured for the specific interconnect device used on the SAN. Other types of data that can be stored on SAN devices include databases, video, and streaming media. On a Storage Area Network using a Fibre Channel interconnect, backups can be performed throughout the workday. Thus, eliminating timely and costly after hours backups. Storage Area Networks eliminate bottlenecks that make it difficult to access data on traditional networks.
Fibre Channel Arbitrated Loop Specification (FC-AL), provides for Loop Initialization Primitives (LIPS) to occur whenever a new device enters the loop (or Fabric as Fabrics often include one or more loops). LIPs are basically messages directing all other devices on the loop to stop the current processing activity because something on the loop topology has changed (i.e., a new device has been powered on, a device has entered or left the loop, etc.). When a LIP occurs, each device updates their internal maps identifying the various devices on the loop. LIPs are necessary because each device on a Fibre Channel loop needs to know target device addresses in order to establish dedicated circuits. When the LIP sequence completes, each device resumes the activity they were performing before the LIP sequence was initiated. In some implementations on a loop or fabric, each time the Fibre Channel adapter for any device is opened or closed, the laser light on the adapter is turned on and off causing another LIP sequence. Increasing the number of devices on the loop exacerbates the condition by causing more LIPs. LIPs interrupt all devices connected to the loop. Often a LIP will be initiated even though the adapter on the LIP-causing device does not enter or leave the loop, only the light on the adapter was toggled causing a LIP condition.
When a device is connected to a Fibre Channel loop, it is in one of two modes—“participating mode” or “non-participating mode.” A device may have multiple logical ports connected to the Fibre Channel loop. A device's logical port is in participating mode when it has acquired a physical address. A device acquires a physical address through an initialization process. A logical port that is in participating mode may voluntarily relinquish control of its physical address and enter nonparticipating mode. This allows another logical port to use the physical address. A device's logical port is in nonparticipating mode when it does not have a valid physical address. Reasons for not having a physical address may be that the logical port was unable to obtain a physical address, the logical port voluntarily does not participate, or the logical port has been bypassed and has recognized a LIP. Nonparticipating mode is the default operational mode for a logical port.
Before a logical port can send data through the Fibre Channel loop, it must arbitrate for the loop. In order to do this, the logical port sends an arbitrate (ARB) message across the loop. A priority scheme determines which logical port receives the loop if multiple nodes request the loop at the same time. When a device's logical port receives ownership of the loop, the device can communicate with another port on the loop.
When a new port wants to enter the loop (enter participating mode), the FC_AL specification states that the device's logical port will send out a LIP indicating such. Any operations that were being performed on the loop are suspended. This means that devices that were transferring data on the loop must stop what they were doing and participate in the initialization sequence. The purpose is to assign a physical address to the new logical port. Next, a device on the loop is chosen as the loop master to manage the, initialization and coordinate the selection of a physical address for the new port. Optionally, a positional map is generated and propagated to all devices on the loop. At this point, the loop master issues a CLS primitive and finally IDLE primitives, which inform the devices attached to the loop that they can resume normal operations. The device that owned the loop before the initialization took place has to arbitrate again for the loop.
The reason the initialization process is performed is because an addition/deletion to the loop is a state change. It may be that a target device was removed from the loop and, consequently, the corresponding physical address disappears. In addition, a target device intended for future communications may have been removed. If initialization was not performed, a device may attempt to communicate with a nonexistent device.
When LIPs occur, the internal state machine of the FC-AL device enters into the OPEN-INIT state, which is the state that is used to deal with initialization/address assignment. When it is doing normal I/O, it is in the “loop circuit” state. The device cannot be in two states at once as the hardware operates in one state at a time. Performing LIPs/address assignment and normal I/O at the same time would require simultaneous use of two states, which is not possible. When the fiber optic laser connected to a device's Fibre Channel adapter turns on and off, the toggled light is interpreted as entering or leaving the loop, thus causing a LIP condition.
In short, state changes on the loop have to be dealt with immediately because they are major events on the loop. State changes can affect current or future I/O operations. The FC-AL protocol allows for only two devices to use the loop at the same time. Interleaving normal I/O messages and LIPs on the loop is not allowed or supported by the protocol.
FIG. 2 shows two devices in the prior art connecting to Fibre Channel Fabric 220. Device 200 is shown in closed 200 status. When a device, such as device 200, is in a closed state, a connection no longer exists between the device and the Fibre Channel fabric. Device 250 is shown being in opened 240 status. Because device 230 is in the open state, a connection exists between it and Fibre Channel Fabric 220. When the connection is open, request 250 can be transmitted to device 230. Device 230 can process request 250 and send response 260 to another device connected to Fibre Channel Fabric 220. Other devices that may be connected to Fibre Channel Fabric include disk storage device 270 and tape device 280.
FIG. 3 shows what happens when device 300 toggles between open state 310 and closed state 320. Other device 360 sends request 330 to device 300 through Fibre Channel Interconnect 350. If device 300 is in open state 310, it processes the request and sends response 340 to a target device through Fibre Channel Interconnect 350. Because other device 360 performs Fibre Channel Re-initialization whenever device 300 toggles between open state 310 and closed state 320, other device 360 does not send request 330 to device 300 when device 300 is in closed state 320. However, having other devices perform Fibre Channel re-initialization each time any device connected to Fibre Channel Interconnect changes states is costly in terms of efficiency and throughput. In fact, certain devices, such as switches, may disconnect a Fibre Channel loop when the number of re-initializations exceeds a threshold, as high numbers of re-initializations may indicate that the loop is experiencing difficulties.
A challenge, therefore, with Fibre Channel connected devices is being able to open and close the Fibre Channel connection without causing a LIP condition to occur. Consequently, what is needed is a system and method for preventing unnecessary Fibre Channel re-initializations.